Of all components in a computer, the central processing unit ("CPU") typically emits the most heat during operation of the computer. This heat is generated because the CPU is the electrical center of the computer. As computer systems grow in speed and shrink in size, power consumed by the CPU per unit volume (power density) increases dramatically. Thus, it becomes evermore important to dissipate the heat generated by the CPU and other heat-intensive components within the computer during operation to ensure that the components remain within their normal operating temperature ranges. Dissipation of heat reduces the chance that the components will fail immediately or have too short a lifetime.
In early desktop personal computers ("PCs"), components were passively cooled by radiation or convection, the surfaces of the components themselves interfacing directly with still air surrounding the component to transfer heat thereto. Unfortunately, air is not a particularly good conductor of heat. Therefore, in the early desktop PCs, the heated air tended to become trapped, clinging as a boundary layer to the components, acting as a thermal insulator and increasing component operating temperature. Eventually, PCs were provided with fans to force air over the surfaces of the components, removing the boundary layer and increasing the temperature differential between the surface of the component and the surrounding air to increase the efficiency of heat transfer. The increased temperature differential overcame some of the poor heat-conducting qualities of air.
As CPU power density continues to grow, it has become common to associate a heat sink with the CPU to increase the heat-dissipating surface area of the CPU for more effective cooling. Such heat sinks have a plurality of heat-dissipating projections or elements on an upper surface thereof. Lower surface of the heat sink is placed proximate the component and a retention clip is employed to wrap around the heat sink, gripping a lower surface of the component with inward-facing projections.
All of the previously discussed cooling methods, however, are premised on the condition that the ambient environmental temperature about the PC is sufficiently low to allow effective heat transfer to take place. For example, if the computer is in an excessively warm environment, there is not a sufficient temperature differential between the environment and the electrical components to effect a cooling of the components. As is well known, heat transfer is a function of temperature differential; and the narrower the differential, the less heat is transferred. Thus, these prior art cooling methods become inadequate to protect the CPU when the ambient environmental temperatures get too high.
In recognition of this problem, the prior art has provided an overtemperature-detection circuit employing a thermocouple that is constructed of layers of different metals. When the thermocouple is subjected to a temperature change, an electromotive force is produced. Electrical leads couple the thermocouple to a current-detection circuit that computes the thermocouple's temperature, thereby detecting indirectly the temperature of the microprocessor. However, this prior art technique suffers from time and cost problems. Thermocouples are expensive, and are yet another component that has to be purchased and installed on the circuit board of the PC, thereby increasing cost and the time it takes to manufacture the PC. In addition, the thermocouple is yet another component of the PC that is subject to failure.
Thus, what is needed in the art is a more time-efficient and cost-effective technique for detecting CPU temperature.